This invention relates generally to methods and apparatus for computed tomography (CT), and more particularly to methods and apparatus that provide for 3D scatter correction.
Cone Beam Multi-Slice Computed Tomography (CT) Systems have wider Z-Axis coverage than traditional MultiDetector CT systems (MDCT). The traditional MDCT systems were limited to beam widths of 20 mm or lower. With the advent of Cone Beam Multi-Slice systems, the new beam width is more than double the beam width of traditional MDCT systems. These new systems are typically more sensitive to the effect of scattered radiation (scatter). Scatter can be described as spurious radiation due to X-rays bouncing off the internal components of the CT system or the object being scanned. The effective correction for scatter is more important when the CT detector is not effectively collimated to reject scattered radiation.
Scatter causes dark shading artifacts and CT Number non-uniformity in the objects being scanned, as well as a CT Number accuracy dependence on object size and aperture width. Very low frequency scatter profile adds a positive bias to the detected radiation signal, thus reducing the effective attenuation of the imaged object, resulting in a negative bias in the measured Hounsfield Units (HU) in images. Coupled with highly varying attenuation profiles of the object being imaged, scatter can cause differential artifacts, such as shading in uniform regions.
Accordingly, it would be desirous to reduce or eliminate the effects of scatter. Therefore, 3D scatter correction methods and apparatus are described below.